A. Technical Field
This invention relates to signal monitoring, and more particularly, to testing high frequency signals on a trace.
B. Background of the Invention
The importance of integrated circuitry is well known. Technological advancements have led to continual reduction in the size of integrated components and circuitry. The electronic devices employing integrated circuitry have not only seen a reduction in their size but also an improvement in signal processing efficiency. One reason for the improvement of signal processing is the use of higher frequency signals that are able to communicate large amounts of data within an integrated circuit.
As integrated circuits have become smaller and signal frequencies within the circuits have increased, the ability to effectively test and measure signals and components within the circuits has become more difficult. For example, it may be difficult for an engineer to locate a failure in an integrated circuit because of the problems in tapping or extracting an electrical signal internal to the integrated circuit. The ever-increasing signal frequencies on IC traces have made it difficult to effectively tap and monitor these internal IC signals. Electromagnetic interferences, including signal reflection and distortion, oftentimes render a tapped signal unusable for monitoring purposes. Furthermore, footprints on a trace that are designed to allow testing of a signal may reduce the performance of the trace by effectively creating a stub on the trace and/or adding unwanted capacitance.
The existing methods of monitoring signals typically include the use of an oscilloscope to probe a signal on a particular trace. FIG. 1 illustrates an exemplary signal monitoring method using an oscilloscope. As shown therein, a driver 102 sends a signal to a receiver 104 through a signal trace 106, which acts as a medium through which the signal travels. A metallic end of a scope probe 108 is brought in contact with the signal trace 106 resulting in a portion of the signal to be diverted onto the probe and sent to the oscilloscope. The signal traversing between the driver and the receiver can thus be tested.
The probe 108 may distort the signal because its metallic contact may function as a stub resulting in added dispersion and reflection to the signal being monitored. If sufficiently high frequency signals are being monitored, this dispersion and reflection on the signal may render an oscilloscope reading of the signal to be imprecise or unusable.
A sub-miniature A (“SMA”) connector may be used to more effectively measure a high speed signal. As illustrated in FIG. 2, “zero ohm” resistors R1 210 and R2 212 may be placed on the trace to allow connection of the SMA connector. It is important to note that a zero ohm resistor may in fact have a small amount of resistance associated with it. During the normal operation of a driver 202 and a receiver 204, the resistor R1 210 is placed in the footprint area specified, while the resistor R2 212 is physically removed. To observe the signal on the PCB trace 206 the resistor R1 210 is then removed and R2 212 placed in the footprint area specified. The signal is directed towards SMA connector 208 to be observed on the scope.
This method reduces the reflections but still adds stub and extra capacitance that are caused by the surface mount footprint on the trace. This stub and capacitance may lead to inaccurate results and distort the signal received by the receiver 204. At specified frequency of operation, which tends to be more than 1 Gbps, the accuracy of the observed results greatly affects the troubleshooting procedure. The extra trace on board in mentioned operating conditions adds to the inaccuracy.
There is a need of a method designed to allow observance of high frequency signals on trace without adding reflections and dispersions into the original signal.